High-efficient wire sawing of GaAs-wafers by utilization of crack nucleation mechanisms

One of the big challenges for wire sawing of semiconductor wafers is warp and waviness, which are mainly caused by wire deflection during cutting process. Therefore, lapping or grinding steps are often used to improve quality but accompanied by additional material losses. The mechanisms of a high quality wire sawing process for compound semiconductors will be presented here. The commonly accepted model for out-of-plane deviation of wires during wire sawing process was expanded by including intrinsic forces in addition to commonly considered technological ones, which are determined by material properties of the semiconductor used. For this the concept of a critical cutting depth for ductile-brittle-transition underlying cutting and grinding processes of brittle materials has been revised. Both Vickers hardness tests and single scratching tests were used to study the ductile-brittle-transition in greater detail. It was found that mainly two types of cracks (called A- and B-cracks) nucleate in GaAs, which are characterized by different threshold loads for their appearance. The effect is related to the existence of two types of dislocations with different PEIERLS-barriers, which dominate in III-V compounds, the 600 a- and b-dislocations. The micro crack nucleation is assisted by pile-ups of these dislocations, which leads to different crack initiation probabilities n for A- and B-cracks at a given load with nA > nB. This effect causes a significant dependence of the critical penetration depth for ductile-brittle-transition from the direction of a moving indenter in scratching tests. This critical penetration depth and the corresponding critical load determines measurable constraint forces, which act on the wire during the sawing process. Under certain well-defined conditions these constraint forces maintain the wire in a stable position perpendicular to the cutting direction, i. e. the out-of-plane-deviation of the wires is near to zero and, consequently, warp and bow will be minimal. This context has been proven by wire sawing experiments at a industrial multi-wire saw and by optical flatness measurements of GaAs-wafers. The result of this investigation was verified in a high efficient wire sawing technology for mass production of 150-mm-GaAs-wafers. Commonly used technological steps like lapping or surface grinding are no longer necessary and, in consequence, the material losses are reduced. Furthermore, the feed rates could be increased up to 400 percent compared to standard wire sawing of GaAs with improved geometrical parameters of the wafers.